An infrared sensor (infrared rays image pickup device) for receiving infrared rays emitted from an object and converting it into an electrical signal can obtain a temperature distribution of the object day and night. Since the infrared rays have higher permeability relative to smoke and mist than that of visible light, the infrared sensor can take an image under a bad condition. Therefore, the infrared sensor has a wide application range such as a defense field, a security camera, a fire detecting camera, and an onboard camera for night vision.
The infrared sensors are divided into two kinds, i.e., a cooling type and a non-cooling type. The cooling type is an infrared sensor for using inter-band transition of a carrier caused by receiving the infrared rays. It is necessary for the cooling type to have a cooler. Therefore, it is difficult to miniaturize the device, and a manufacturing cost increases. Therefore, the use of the infrared sensor of the cooling type is limited to a specific field.
Whereas, the non-cooling type is a thermal infrared sensor which is a so-called bolometer. The non-cooling type has a mechanism to convert the received infrared rays into heat and convert the heat into the electrical signal. Since the non-cooling type can operate at room temperature, it is not necessary to have the cooler. Therefore, the non-cooling type device can be easily miniaturized and can keep the manufacturing cost lower. Accordingly, the non-cooling type is widely used compared with the cooling type.
Since the temperature of the non-cooling type infrared sensor changes according to the environmental temperature, the non-cooling type infrared sensor is affected by the environmental temperature. In order to remove the effect by the environmental temperature, the non-cooling type infrared sensor outputs a signal in which a signal by the reference pixel for not reacting to the infrared rays has been subtracted from a signal by the heat-sensitive pixel for reacting to the infrared rays.
It is necessary for the reference pixel not to react to the infrared rays, and in addition, it is necessary that the change of the electrical characteristics relative to the change of the environmental temperature of the reference pixel coincide with that of the heat-sensitive pixel. This is because the output of the infrared sensor is changed according to the environmental temperature when the change of the electrical characteristics relative to the change of the environmental temperature of the reference pixel does not coincide with that of the heat-sensitive pixel. However, it has been difficult to realize both non-sensibility to the infrared rays and the consistency with the electrical characteristics of the heat-sensitive pixel.
For example, as a method to realize the non-sensibility to the infrared rays, a pixel structure, that is, a thermal black pixel (TB pixel) has been proposed. The thermal black pixel instantaneously releases the heat generated by the received infrared rays to a side of a substrate while receiving infrared rays. However, there is a possibility that the electrical characteristics of the reference pixel are different from that of the heat-sensitive pixel when the TB pixel is used as the reference pixel.
As an another method, an optical black pixel (OB pixel) has been proposed. In the optical black pixel, a part of the heat-sensitive pixels is shielded by a light shielding film. When the OB pixel is used as the reference pixel, the structure of the reference pixel can be the same as that of the heat-sensitive pixel. Therefore, the electrical characteristics of the reference pixel can be coincided with that of the heat-sensitive pixel. However, it is difficult to completely shield the infrared rays. The OB pixels are influenced by incident infrared rays with high energy and cannot function as reference pixels.